This invention relates to a hydraulic control method for a trial hydraulic press in the press industrial field, in which a tryout of a metal mold for a mechanical press suitable for mass production is carried out with a hydraulic press in accordance with the same motion curve as that of the mechanical press so as to reduce metal mold corrections at a job site as much as possible.
Many of small-sized to large-sized goods on the market are produced by press molding. A so-called mechanical press, such as a link press, a crank press, or an eccentric press, is used especially for mass production by press molding.
In order to manufacture or correct a metal mold for such goods, it is preferable to use the same mechanical press as a press used in actual production, but a hydraulic type trial press has been used because the mechanical press is expensive or the mechanical press cannot be easily operated when the metal mold is corrected.
However, when the metal mold that has been manufactured or corrected with the conventional hydraulic type trial press is attached to the mechanical press for molding, the cases frequently occur in which a part of the molding materials is damaged or a molded article cannot have a uniform thickness, so that molding cannot be satisfactorily carried out. For this reason, the metal mold is corrected by shifting between the trial press and the mechanical press. However, this entails much labor and time for correcting the metal mold.
This cause can be ascribed to the difference in speed between the slide of the oil hydraulic press and the slide of the mechanical press, and therefore the press motion curve of the hydraulic press is required to coincide with the press motion curve of the mechanical press.
The present applicant researched and developed a method to achieve a tryout of the metal mold by the hydraulic control so that the slide of the hydraulic press matches the processing speed of the mechanical press. As a result, a great improvement has been brought about, but there still exists a problem in furthering improvements to coincide with a press motion curve peculiar to each individual mechanical press.
Additionally, in recent years, materials that are difficult to mold, such as high tensile steels or aluminum materials, have appeared, and therefore a press of which a metal mold can be easily manufactured and corrected has been demanded.
The present invention is devised in the light of the above background, and to solve the above problems. It is therefore an object of thereof to provide a hydraulic control method for a trial hydraulic press in which a plurality of pressure cylinders with necessary output are disposed in parallel or axisymmetrically so that a metal mold for a mechanical press can be manufactured and corrected, an adequate amount of oil capable of obtaining a press motion curve of the mechanical press in accumulators is accumulated so that a predetermined amount of oil can be supplied to a plurality of pressure cylinders of the hydraulic press when trial molding is carried out, each directional control valve to an oil supply circuit thereof is connected so that hydraulic oil can be selectively supplied to a plurality of pressure cylinders that have been disposed in parallel or axisymmetrically, a servo valve is disposed so as to freely adjust the amount of oil, hydraulic oil is supplied to a predetermined cylinder of a plurality of pressure cylinders by opening a predetermined directional control valve, and the pressure cylinders are hydraulically controlled by the servo valve so as to obtain a coincidence with a press motion curve of the mechanical press with predetermined output.
Thereby, even in the hydraulic press, a metal mold used in the mechanical press is manufactured, corrected, and tried such that an accumulator is pre-filled with adequate hydraulic oil, and a slide is subjected to hydraulic control so as to match the press motion curve of the mechanical press with predetermined output. Therefore, reciprocative corrections of the metal mold between the hydraulic press and the mechanical press for production can be reduced as much as possible.
Especially, hydraulic oil is supplied to a predetermined pressure cylinder of a plurality of pressure cylinders that have been disposed in parallel or axisymmetrically, and thereby the slide speed can be obtained so as to coincide with the press motion curve of the mechanical press with predetermined output.
For example, hydraulic oil is concentrated on pressure cylinders disposed at the center side of a plurality of pressure cylinders, or hydraulic oil is supplied to pressure cylinders disposed on both sides thereof, and thereby the high slide speed of the mechanical press can be obtained so as to coincide with the press motion curve of the mechanical press with predetermined output.
It is another object of the present invention to provide a hydraulic control method for a trial hydraulic press in which a coincidence is obtained with a predetermined press motion curve of a mechanical press ranging from a start position of a pressing stroke of a slide of the hydraulic press to the lower limit position thereof.
Thereby, it becomes easy to obtain a coincidence with the press motion curve of the mechanical press with predetermined output for the above-mentioned hydraulic press.
It is still another object of the present invention to provide a hydraulic control method for a trial hydraulic press in which a pressure cylinder is subjected to control by means of a servo valve so as to obtain a coincidence with a slide speed at each position of a slide on the basis of a press motion curve of the mechanical press serving as a crank press, an eccentric press, a link press, a toggle press, or a combination of these presses.
Thereby, even in a mechanical press, such as a crank press, an eccentric press, a link press, a toggle press, or a combination of these presses, it becomes easy to obtain a coincidence with a press motion curve with predetermined output that corresponds thereto, and the corrections of the metal mold can be reduced as much as possible.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter.